Metallogenic Mechanism Research Articles

Deep metallogenic mechanism in southeastern Chinabased on receiver function data

Crustal deformation and deep metallogenic mechanisms in southeastern (SE) China are still debated. In this study, we applied the receiver function method to measure crustal thickness and Poisson's ratio for crustal rock using teleseismic data recorded at 207 seismic stations from China Earthquake Administration Network. The results showed that crustal thickness varied from ~27 km in the eastern part to ~43 km in the western part of the study area, with an average crustal thickness of 31 km. The crust is thick in the west and thin in the east. The observed Poisson's ratio for crustal rock was relatively high in the southern Cathaysia Block (CB), with an average of 0.295, while in the Qinling—Dabie terrane, it was relatively low, with an average of 0.257. In the middle of the Yangtze craton and central east of the CB, Poisson's ratio for crustal rock varied from 0.257 to 0.286. By comparing Poisson's ratio of the intrusive deposits with that of igneous rocks in volcanic complexes, we deduced that the metallic mineral system might be associated with orogenic and hydrothermal deposits. These results indicated that multistage magma and mineralization in the study area might be attributed to the tectonic-magma-thermal event. The high Poisson's ratio for crustal rock in the southeastern margin of the CB and northeastern Upper Yangtze Cratonmight be related to Mesozoic lower crustal mafic partial melt, which provides an important environment for various magmatic intrusions and metallogenies.

Critical metals in sediment-hosted Pb-Zn deposits in China

<p indent=0mm>Sediment-hosted Pb-Zn deposits are mainly comprised of Mississippi Valley-type (MVT) deposits situated in carbonate-dominated sedimentary rocks and clastic-dominated (CD) deposits located in siliciclastic-dominated sequences. They are significant sources of critical metals such as cadmium, gallium, and germanium, as well as indium, cobalt, and thallium. In China, sediment-hosted Pb-Zn deposits are found in 5 metallogenic belts/districts, namely the Sanjiang belt, the Yangtze Block district, the Tarim Craton district, the Changba belt, and the Langshan belt. They provide 54% of China’s Pb-Zn resources, but their resource endowment and the metallogenic characteristics of these associated critical metals remain unclear. After briefly reviewing the main critical metals in sediment-hosted Pb-Zn deposits and sediment-hosted Pb-Zn deposits in China, this review summarizes the distribution and enrichment mechanisms of critical metals in sediment-hosted Pb-Zn deposits in China and recommends future research. These critical metals are unevenly enriched in sediment-hosted Pb-Zn deposits in China. Compared to the crustal elemental abundances, Cd, Ge, and In are the most enriched, Tl and Co have lower enrichment degrees, and Ga has the lowest enrichment degree. Cd, Ga, Ge, and Tl are rich in MVT deposits, while In and Co are rich in CD deposits. In all five sediment-hosted Pb-Zn belts/districts, Cd is relatively abundant. However, other critical metals are enriched to a different degree in each belt/district. In terms of distribution, Cd is well enriched in all five sediment-hosted Pb-Zn belts/districts, particularly in the Sanjiang belt of the Qinghai-Tibet Plateau, and the Yangtze Block district; Ge is most abundant in the Yangtze Block district, followed by the Changba belt in the Qinling orogenic belt, and Sanjiang belt; In and Co are enriched in the Sanjiang belt, followed by the Yangtze Block district and the Changba belt; Tl is enriched in the Sanjiang belt, the Yangtze Block district, and the Changba belt; and, Ga is most enriched in the Changba belt and Yangtze Block, followed by the Sanjiang belt. Based on these characteristics, two enrichment mechanisms are occurring in sediment-hosted Pb-Zn deposits. First, sediment-hosted Pb-Zn deposits are selective for the enrichment of critical metals, and second, the degrees of enrichment of critical metals in these deposits are different. The first enrichment mechanism results from the similarity in physicochemical properties between the critical metal elements and dominant elements (such as Zn and Fe) in the ore and gangue sulfides (such as sphalerite and pyrite). The second mechanism is associated with substitution forms of critical metal elements and host minerals, as well as physicochemical conditions and tectonic conditions of the deposits and tectonomagmatic processes throughout geological history. Research into critical metals in sediment-hosted Pb-Zn deposits in China abounds in the Yangtze platform Pb-Zn metallogenic belt and MVT Pb-Zn deposits; however, this research is still in the pipeline. A database of critical metal resources hosted by sediment-hosted Pb-Zn deposits in China is urgently needed, as is comprehensive research into the metallogenic mechanism of different critical metals, and the determination of the regional metallogenic regularity of these critical metals.

Relations between pyrite morphologies and uranium mineralization in the Shuanglong region, northern China

Pyrite is widely distributed in ore-hosting sandstones of the Zhiluo Formation in the Shuanglong uranium deposit in the southern Ordos Basin, northern China. Sandstones from the uranium-bearing stratum was collected to analyze morphologies of pyrite and its relations with uranium mineralization by means of scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS). The results show that colloidal and framboidal pyrite, and pentagonal dodecahedron microcrystalline widely occur in sandstones, and uranium minerals are unevenly distributed around pyrite. According to the occurrences of pyrite, morphologies of pyrite are orderly evolved from microcrystalline, and the formation of pyrite is grouped into four periods. Moreover, the pyrite might preferentially or simultaneously precipitate over uranium minerals. The smaller the diameter of pyrite, the more favorable for uranium enrichment. Additionally, variation trends of U contents are opposed to those of the Fe and S contents as well as the Fe/S atomic ratios. Moreover, the decrease rate of S contents is greater than that of Fe contents. It indicates that S and Fe from pyrite both play roles in uranium mineralization, and the S contribution dominates over the Fe contribution. Additionally, the aforementioned conclusion is also supported by the existences of Fe (III), S, SO32-, and SO42. Compared with carbonaceous debris (CD), pyrite might play a dominant role in uranium enrichment. During the process of enrichment and reduction of uranium by pyrite, CD might provide beneficial reducing environment for precipitation and preservation of pyrite and uranium minerals. The study could provide guide for understanding metallogenic mechanism to some extent.

Mineralogical and geochemical research on Pengyang deposit: A peculiar eolian sandstone-hosted uranium deposit in the southwest of Ordos Basin

The newly discovered Pengyang uranium prospect area in the southwest of the Ordos Basin is the world's first uranium deposit hosted in eolian sandstone, which overturned the conventional view of uranium mineralization in fluvial-delta sedimentary strata. Uranium ore body occurring as tabular or lens-shaped is hosted in the gray-green reductive eolian sandstone of Lower Cretaceous Luohe Formation at depths ranging from 700 m to 3000 m. The host eolian sandstone is characterized by the typical high angle cross-bedding, wind sand ripple and grainflow strata. In this study, we conducted borehole log, petrographic observation, whole rock geochemistry analysis, geochemical and mineralogical study of uranium occurrence (SEM), element mapping of uranium minerals and in-situ sulfur isotope determination of pyrite by LA-MC-ICP-MS to reveal the uranium enrichment mechanism. The observations by SEM show that the predominant uranium mineral is pitchblende, primarily occurring as aggregates of nano to micro crystals absorbed on amorphous TiO2 or as colloform replacing the detritus Fe-Ti oxide minerals, both demonstrating the excellent absorption property of small particles of anatase. The contents of altered minerals such as chlorite and pyrite in gray-green sandstone increased significantly under scanning electron microscope (SEM). Whole rock geochemistry analysis data of sandstone samples collected in the target layers display the strong positive correlation between U and S. Whereas, in the elements mapping images, uranium enrichments display complete dissociation with pyrite as the uranium contents adjacent to or around the pyrite grains are under detection limit, demonstrating that uranium precipitation likely occurred earlier than the sulfuration of red eolian sandstone. Sulfur isotope of the two morphological types of pyrite are both characterized by a relatively light signature, ranging from − 19.23 to − 27.22 ‰ and from − 21.60 to − 29.64‰ respectively, implying that they are generated from bacterial sulfate reduction in the open systems with an adequate supply of sulfate. Anaerobic sulfate-reducing bacteria use the hydrocarbon transferred along faults to the sandstone as energy to reduce sulfate (SO42−) to H2S. In addition to the typical vertical red - yellow - gray color zonation, we also observed distinct reverse color zonation of sandstone, which can hardly be interpreted by traditional interlayer-oxidation-zone theory. We attribute the uranium reduction to the encounter of downward penetrating oxygenated groundwater with the upward migrating oil and gas conducted by thrust faults, which are widespread distributed in the west margin of the Ordos Basin. This study gives a new insight into uranium metallogenic mechanism in eolian sandstone and underpins an effective vector for the exploration of sandstone-type uranium deposits in the western of the Ordos Basin.

Intrusion-related orogenic gold deposit in the East Kunlun belt, NW China: A multiproxy investigation

The Wulonggou gold district is one of the most important gold producers of the East Kunlun metallogenic belt in China. Due to its complex geological background and limited investigations, the age of mineralization and ore-forming process remain unclear. Here, we focus on the Yanjingou gold deposit which is the largest and most typical deposit in the Wulonggou gold district, with a view to investigate the metallogenic mechanism and timing of ore formation with a view to evaluate the ore-forming processes and sources through a comprehensive study of the ore mineralogy, monazite and zircon U-Pb dating, in situ trace element analysis and mapping, and in situ S isotopes. Our results show that the magmatism and mineralization were coeval, during 239 Ma and 244 Ma in the Middle Triassic. Four stages of mineralization are identified with distinct textures, mineral assemblages, trace element characteristics and S isotopes. Stage 1 is represented by euhedral pyrite bearing quartz veins, which originated from deep metamorphic fluid, and was rarely affected by magmatic hydrothermal fluids. Stage 2 is characterized by the occurrence of abundant oriented arsenopyrite, which originated from the mixture of deep metamorphic fluid and magmatic hydrothermal fluid. Stage 3 is characterized by the occurrence of polymetallic sulfide of copper, with two generation of pyrite (stage 3 Py1 and Py2). Stage 3 Py1 formed from magmatic hydrothermal fluids whereas Py2 originated from deep metamorphic fluid and was also slightly influenced by magmatic hydrothermal fluids. Stage 4 is represented by late calcite and pyrite combination, which originated from another stage of deep metamorphic fluid. Stage2 and 3 are the main gold mineralization stages, and Au has a close relationship with As, and an obvious inverse correlation with Co and Ni. Combined with the trace element characteristics, we infer that the denudation degree of the Yanjingou gold deposit is very shallow with good prospects for exploration. Through multi-proxy investigation of the different stages and types of pyrite, we postulate that the Yanjingou gold deposit is an orogenic gold deposit related to intrusive rocks formed during Middle Triassic compressional transformation.

CSAMT constraints on the metallogenic mechanism of the Zhaishang gold deposit, West Qinling, China

Whether the ore-forming fluids and materials of Zhaishang Carlin/Carlin-like type gold deposit were derived from concealed Mesozoic intermediate–acidic intrusive rocks through deep faults is controversial. In this study, eight CSAMT profiles were used to investigate the electrical resistivity structure of this deposit using high-resolution 2-D inversion. A ∼1 km wide high-resistivity (>3000 Ωm) body was observed at the base of the resistivity model (∼600 m). Two slightly NE-dipping high-conductivity channels were also observed along two sides of the high-resistivity body that connected to the gold-bearing quartz veins at the surface. The data suggest that the high-resistivity body is a Mesozoic granite and the two high-conductivity channels are fault zone conductors, which may be the wings of an NE-trending anticline that formed under regional compressive stress during the Caledonian orogeny. Their reactivation during the Indosinian and Yanshanian periods likely formed conduits for rising deeply-sourced ore-forming fluids (likely magmatic water). These conduits also promoted ground and meteoric water infiltration and mixing with the rising fluids. Accordingly, at least some of the ore-forming fluids and materials in the Zhaishang deposit were derived from Mesozoic granites through concealed faults, which can provide new geophysical constraints for discussions of the deposit’s metallogenic mechanism.

Contribution of microbial processes to the enrichment of Middle Permian manganese deposits in northern Guizhou, South China

Economically important manganese deposits are hosted in the Middle Permian Maokou Formation of Zunyi, northern Guizhou, South China. During the Middle Permian, the intense rifting related to the initial stage of the Emeishan Large Igneous Province (ELIP) led to the development of carbonate platforms and inter-platform troughs. The manganese deposits occur in the transitional zone between carbonate platforms and troughs. Previous studies emphasized that the hydrothermal activities at the bottom of the trough basin controlled the formation of manganese deposits. In this study, new sedimentary, mineralogical, and stable isotope evidence are acquired from this manganese deposit, indicating that the microbially-mediated metallogenic mechanism also made an important contribution for the Middle Permian manganese deposition. The metallogenesis of this manganese deposit is highly like the combination of hydrothermal and microbial processes. Manganese ores in Zunyi are manganese carbonate, showing massive and clastic structures, no macroscopic nor microscopic lamination are found, samples are coarse-grained, diagenetically recrystallized with abundant mineralized microbial and microfossil biosignatures. FTIR, EPMA, and Raman analyses recognize micrometer-scale cyclic mineralogical assembly and help reconstruct the proposed new model of microbial manganese metallogenesis. Hydrothermal activity in the basin provided dissolved Mn2+ ions into the anoxic basal watermass. In the syngenetic stage, microbial systems could be subdivided into three categories: (1) cyanobacterial system, (2) Mn-biomat system and (3) Fe-biomat system. Cyanobacterial activity led to the precipitation of calcite, and it could be partially affected by Mn-metasomatism and transformed to Mn-bearing calcite. Mn-oxidizing microbes led to the precipitation of manganese bio-oxide (δ-MnO2) near the redoxcline of the basin. Fe-biomat system was responsible for the precipitation of Fe-oxides (hematite) and Fe-hydroxides (ferrihydrite and lepidocrocite). After burial, manganese oxides reacted with the organic matter in the sediments through the microbially-mediated processes during the early diagenesis and the Mn-metasomatism of the cyanobacterial carbonate jointly contributed to formation of early diagenetic manganese carbonate ore. The redox fluctuations between oxic/suboxic and anoxic zones led to the re-oxidation process and resulted in cyclic marcasite. Anatase cycles observed in samples were interpreted as the diagenetic product of Fe-biomat system.

Microbial metallogenesis of early carboniferous manganese deposit in central Guangxi, South China

Manganese deposits in the Early Carboniferous Baping Formation of central Guangxi, South China were formed in the Youjiang Basin on the southern passive margin of the South China Block. Hosted in the Second Member of the Baping Formation, the manganese ore layers were interbedded by thin-middle manganese carbonate and silicified carbonate. Previous studies provide limited information about this manganese deposit, and the sedimentary characteristics of ores and the metallogenic mechanism are not clear. In this study, integrated analyses of petrology, mineralogy, geochemistry, and carbon isotope reveal microbial metallogenesis in the Early Carboniferous manganese deposit of central Guangxi for the first time. Oncoid-bearing massive Mn carbonate and laminated Mn ore contain evidence of disseminated mineralized microbial biosignatures in millimeter scale. An in situ mineralogical study based on CL, FTIR, SEM-EDS and Raman spectroscopy has identified the syngenetic and diagenetic Mn and Fe systems during the formation of the manganese deposit. Both were formed by biomats and precipitated micro-laminae of microbiogenic minerals such as Mn-calcite, rhodochrosite, kutnohorite, and apatite. The metallogenic model of the manganese deposit in the Baping Formation can be divided into two main stages: (1) Sediment accumulation stage, where enzymatic Mn(II) oxidation controlled the accumulation of Mn oxides within the cyanobacterial organic and carbonate network, thus enriching the manganese; (2) Diagenetic stage, where Mn-metasomatism of microbial carbonate and the reaction between syngenetic manganese oxides and the organic matter led to the precipitation of proto-ore (Ca-rhodochrosite). A positive δ13C value (+1.53‰) within the Mn carbonate sample and negative δ13C values (−7.15‰ to −3.64‰) in Mn ore samples indicate the participation of organic carbon in the alkalinity source of Mn-bearing carbonates. The presence of kutnohorite and of Mn-sulfide minerals indicates a transitional zone between suboxic and anoxic conditions. Anatase represents the diagenetic mineral of Fe-biomat. After release of elements in the decomposed cells and EPS, a series of accessory minerals (feldspar, apatite, pyrite, etc.) formed.

Stable isotope and fluid inclusion constraints on the source and evolution of ore fluids in the Xiuwacu W-Mo granite-related quartz-vein deposit, Yunnan Province, China

The Xiuwacu granite-related quartz-vein type W-Mo deposit (9.16 million metric tons at 0.26% WO3 and 0.27% Mo) is situated in the South Yidun terrane (SYT) in SW China. Orebodies, together with aplite veins, occur mainly along the NW-SE-trending fault systems within the Xiuwacu complex intrusions. However, the metallogenic mechanism of this deposit is still ambiguous. In this study, three stages for the ore-bearing quartz veins have been recognized based on the field and petrographic observations: (1) pre-ore fluorite-quartz; (2) syn-ore scheelite-quartz; and (3) post-ore calcite-quartz assemblage. The average δ34S value is 3.84‰, combination with the molybdenite Re values (4.3–18.6 × 10−6), indicating that the ore-forming fluid derived from lower crust magmatic fluid. The δD and δ18Ofluid values of the ore-forming fluids in the Xiuwacu deposit vary broadly from −104.9‰ to −75.0‰ and from −2.5‰ to +5.9‰, respectively, indicating a mixture of magmatic and meteoric water or seawater during the ore-forming process. The coexisting quartz with scheelite contains two-phase aqueous inclusions (type Ia), minor two-phase vapor inclusions (type Ib) and two- or three-phase CO2-bearing inclusions (type II), while scheelite only contains two-phase aqueous inclusions (type Ia). The homogenization temperatures for fluid inclusions in scheelite are very similar in both mineralized zones, which are slightly higher than those in quartz in the East mineralized zone, but are slightly lower than those in quartz in the West mineralized zone. These indicate that fluid cooling is predominant in the formation of scheelite. As the homogenized temperatures in the fluid inclusions of scheelites have a normal distribution, together with the medium-coarse grained signatures of scheelite, it could be concluded that Ca supply was insufficient during the tungsten precipitation process. Thus, the ore-forming mechanism of the Xiuwacu deposit is controlled by both the simple fluid cooling and addition of Ca during fluid mixing and/or fluid-rock interaction.

Metallogenic Characteristics and Formation Mechanism of Naomugeng Clay-Type Lithium Deposit in Central Inner Mongolia, China

A newly discovered Naomugeng lithium mineralization area is located to the east of the Central Asian Orogenic Belt (CAOB). The lithium is hosted in the volcanic rocks of the Manketou’ebo Formation. The altered volcanic rocks mainly consist of quartz, orthoclase, chlorite, montmorillonite, calcite, and dolomite. Here, we present integrated studies of petrography, mineralogy, and geochemistry of the altered volcanic rocks (with an average Li2O content of 0.43 wt.%) collected from the drilling hole and trail trench to systematically investigate the occurrence of lithium, the mineralizing processes, and the metallogenic mechanisms. The secondary minerals of the core samples are montmorillonite, chlorite calcite, and dolomite, while the secondary minerals from the earth surface ones are montmorillonite, chlorite, and calcite. The mass change calculation and isocon analysis show that the rocks received MnO, P2O5, Co, Ni, Cu, and Li and lost Na2O, K2O, MgO, rare earth elements (REE), and Rb in the alteration process. However, other elements such as Fe, V, Co, and Ca of the core samples increased while those of the earth surface ones did not change by much. Hence, there are two zones of alterations, i.e., the montmorillonization-chloritization zone and the montmorillonization-chloritization-carbonatization zone. Lithium enrichment occurs in the zone where montmorillonization and chloritization occur. The lithium is probably enriched in altered minerals such as montmorillonite and chlorite in the forms of interlayered or adsorbed ions. The slightly negative to positive Eu anomalies of the rocks can be explained by the metasomatism of hydrothermal fluid that enriched Eu. We suggest that the Naomugeng deposit is a clay-type lithium deposit and formed under a caldera setting. The meteoric and hydrothermal fluids leach the lithium from the volcanic materials and then alter the host rocks (e.g., tuff or sediments) in the caldera basin, which forms the type of lithium clay deposit. This study analyzed the migration behavior of elements in the Naomugeng lithium deposit during a hydrothermal process, which shows that the mass balance calculation has good application in reflecting the mineralization process of clay type deposit. This study also reveals the great exploration potential of the Naomugeng deposit and has important significance for further prospecting of clay-type lithium deposits in central Inner Mongolia.

Seismic pumping for mineralizaiton in southern Fujian, Cathaysia Block: New insights from a teleseismic full waveform inversion

It is crucial to image the crustal velocity structure with higher resolution to understand the relationship between crustal seismicity and metallogenic mechanisms, which remain challenging targets for conventional seismic tomography. Teleseismic tomography via body-waves can image velocity well in the upper mantle, but poorly in the crust. In this study, we have developed a teleseismic full waveform inversion (TFWI) method based on the frequency-wavenumber spectral element method (FK-SEM) hybrid to improve the resolution of teleseismic P-waves in the crust. We used the TFWI method to study the crustal velocity by using two large teleseismic events recorded by 29 portable stations with ~5 km intervals across the Zhenghe-Dapu Fault (ZDF) in the Cathaysia Block. This is the first attempt using the FK-SEM hybrid on real data. As expected, we obtained a 2D velocity model in the crust that had high lateral resolution. There is an obvious low velocity zone (LVZ) in the crust below east side of the ZDF, while a relatively high velocity anomaly exits within its west side. Combined with previous geochemical and geological results, this LVZ is explained as remnant magma due to the large-scale magmatism in the Late Jurassic and Early Cretaceous. According to the spatial correlation among the LVZ, local earthquakes, faulting, and major ore deposits, we consider that seismic pumping might be a mechanism of thermal fluid transport for the mineralization.

Crustal electrical structure and deep metallogenic mechanism in the Xiongcun and Niangre districts of the Tibetan Plateau

The Gangdese metallogenic belt in the Tibetan Plateau hosts many large ore deposits, of which the Xiongcun and Niangre ore concentration districts are two typical examples. Due to the insufficient geophysical evidence about the deep metallogenic dynamics across these two districts, the electrical structure was obtained by modeling magnetotelluric data to study the relationship of the crustal structure and metallogenic dynamics. Although the mineralization occurred in the past, the continuous magmatic activities after the mineralization could reactivate the previous migration channels to remain some traces, which can be revealed by some geophysical methods. The resistors at depths of less than 20 km may represent the multiple overlapping volcanic rocks related to a serious of magmatic events in the Lhasa-Gangdese terrane. Some conductors that revealed at different depths may be related to the partial melt, aqueous fluids and/or formation of metallic minerals, and were also further indicated as the possible magma chambers. Connecting the conductors at different depths may be further indicated as some ancient migration channels which were probably related to the shear zones and faults. As the ore deposits in both districts belonged to the magmatic-hydrothermal type, the upwelling magma played a crucial role in the metallogenic dynamics. These possible magma chambers at different depths and channels may be also related to the evolution and emplacement of the deep-seated magma, and contributed to the mineralization of both districts. This study can also offer a reference of significance for the deposits in the eastern Gangdese metallogenic belt.

Metallogenic mechanism of large manganese deposits from Permian manganese ore belt in western South China Block: New mineralogical and geochemical evidence

The Permian manganese (Mn) ore belt lies in western South China Block, and contains many large-medium Mn deposits. However, the genesis and metallogenic mechanism of these deposits remains a matter of debate. Here we shed light on this issue based on new mineralogical, geochemical, and Sr isotope data from the Changgou Mn deposit in the Zunyi orefield (Guizhou, SW China). The Mn orebodies occur as lenses and layers, and are hosted in carbonaceous-siliceous limestone, carbonaceous mudstone, and tuffaceous claystone. The ores show a variety of structures (e.g., detrital, brecciated, massive, and banded) and complex mineral compositions (e.g., galena, sphalerite, siegenite, molybdenite, barite, rutile, and monazite). The ore samples are characterized by chalcophile and siderophile element enrichments, low Al2O3/TiO2 ratios (mean 10.36), high and varying Mn/Fe ratios (1.26–4.71), distinctly high REY (rare earth and yttrium) contents (mean 766.46 ppm), and high La/Ce (mean 1.04) and low Y/Ho (mean 28.17) ratios. The footwall and ore samples have 87Sr/86Sr ratios of 0.706897 to 0.707093. Integrated mineralogical and geochemical signatures indicate that the ore-forming fluids were most probably originated from hydrothermal activities related to early-stage Emeishan Large Igneous Province (ELIP) subaqueous volcanism. Redox proxies reveal that sedimentary conditions evolved from euxinic-anoxic (footwall deposition), through anoxic-suboxic (Mn mineralization), to oxic (hanging-wall deposition). Such changes were probably resulted from a coeval eustatic sea-level drop and enhanced seawater oxygen supply. Manganese was likely initially enriched in form of Mn2+, and subsequently precipitated with oxidation, and then transformed into Mn carbonate during sediment diagenesis. To conclude, the tectono-hydrothermal activities and major environmental redox changes led by the ELIP volcanism have provided a favorable source-migration-sink system for the Mn mineralization.

Characteristics of biotite-pegmatitic ore and metallogenic mechanism of uranium in the Husab uranium deposit, Namibia

湖山铀矿床位于纳米比亚达马拉造山带的南部中央带，属于伟晶岩型铀矿，是世界上最大的铀矿床之一。目前关于不同矿石中铀元素的富集与沉淀机制还存在一定争议。为了厘清岩浆演化过程与铀成矿作用的关系，本文对湖山铀矿床内E型伟晶岩型矿石开展了岩石学、矿物学和地球化学研究。野外调查及镜下鉴定结果表明，产铀的E型伟晶岩可以分为"简单类型"矿体和"复杂类型"矿体：前者具有花岗伟晶结构，工业铀矿物为晶质铀矿(含少量铀钍石)，呈浸染状分布于石英、长石和黑云母之间，矿化程度低到中等；而后者表现出非均匀的结构特征，晶质铀矿在成因上与大量黑云母团块有空间联系，矿化程度极高。地球化学研究表明，在"简单类型"伟晶岩中，铀元素的富集受控于分离结晶作用，而在"复杂类型"伟晶岩中，铀矿化与同化混染作用密切相关。矿石的矿物-熔体相平衡模拟结果显示，外来基性组分(FeO、MgO、TiO₂)的混入导致"复杂类型"伟晶岩熔体中矿物的结晶顺序发生了改变，相比于"简单类型"伟晶岩熔体，黑云母初始结晶温度的升高和钾长石初始结晶温度的降低为黑云母提供了更充足的结晶时间和生长空间，促使黑云母以团块状聚集的形式产出。该过程会大量消耗岩浆中的F离子，引发UF_m^4-m络合物的水解，促使晶质铀矿在团块黑云母的附近沉淀，形成高品位的铀矿化。因此，本文有关"简单类型"和"复杂类型"伟晶岩矿石的研究，有效地揭示了矿化过程，丰富了伟晶岩型铀矿床理论，为推动铀矿勘查与开发提供了科学依据。

Ar-Ar chronology of the brittle deformation age for the ore-controlling shear zones in the Jiaodong Peninsula and it's constrains on gold mineralization

胶东地区是典型的剪切带型金矿集中区，精确厘定该地区控矿剪切带的活动时代，可为探讨剪切带与金矿成因关系提供关键的时限约束，并且对矿床成矿模式的建立具有至关重要的意义。大量矿床地质证据显示胶东地区控矿剪切带中脆性变形活动对金矿体的形成具有直接影响，但其脆性变形时代尚不十分清楚。据此，本文在详细研究金矿体赋存特征的基础上，系统选取胶东焦家、玲珑、邓格庄、乳山这四个金矿区控矿剪切带断层泥中白云母进行⁴⁰Ar-³⁹Ar年代学研究。定年结果显示，胶东地区焦家剪切带、招平剪切带以及牟乳剪切带的脆性变形时代分别为110.3±1.5Ma、122.8±1.7Ma、119.6±1.2Ma~115.8±1.4Ma。其中焦家剪切带的脆性变形时代明显晚于招平和牟乳剪切带，可能代表了焦家蚀变岩型矿化形成后易遭受后期的构造叠加。综合胶东各金矿区控矿剪切带变形时代、岩体侵位时代、成矿时代及剪切带活动特征和矿体产出特征，本文认为在多期岩体侵位以及控矿剪切带递进变形过程中，剪切带韧性变形区中由高压流体作用产生的同期脆性破裂可形成脉型矿化，如乳山金矿；而在脆-韧性和脆性变形区中发生的大规模脆性变形可导致脉型和蚀变岩型矿化的形成，如玲珑、邓格庄和焦家金矿。但随着剪切带的递进变形和隆升剥蚀，后期多期次的脆性构造变形叠加，可导致多种矿化类型出现在同一构造部位，如焦家金矿中石英脉型和蚀变岩型矿化。;Jiaodong Peninsula is a typical concentration area for shear zone type gold deposits. Accurate determination of the deformation age of ore-controlling shear zones in this area can provide a key time limit for exploring the relationship between shear zones and the genesis of gold deposits, and is of vital significance to the establishment of metallogenic mechanism. A large number of geological evidences show that the formation of gold orebodies is directly controlled by brittle deformation activities of ore-controlling shear zones in Jiaodong Peninsula, but this deformation age is still unclear. Based on detailed study of the occurrence characteristics of orebodies, we systematically selected muscovite samples from fault gouge in Jiaojia, Linglong, Denggezhuang and Rushan gold mining areas for the Ar-Ar chronology study. ⁴⁰Ar/³⁹Ar dating results show that the brittle deformation ages of Jiaojia, Zhaoping and Muru shear zones in Jiaodong Peninsula are 110.3±1.5Ma, 122.8±1.7Ma and 119.6±1.2Ma~115.8±1.4Ma, respectively. Among them, the brittle deformation age of Jiaojia shear zone is obviously later than those of Zhaopin and Muru shear zones, which may represent that the altered rock type mineralization in Jiaojia deposit is susceptible to structural superposition in the later period. Comprehensively comparing shear zone deformation ages, pluton emplacement ages, metallogenic ages, shear zone activities and orebody occurrence characteristics in Jiaodong gold deposits, it is suggested that: (1) The contemporaneous brittle fractures caused by high-pressure fluids in ductile deformation region of shear zones can lead to the formation of vein type mineralization, e.g. Rushan gold deposits; (2) Large-scale brittle deformation in brittle-ductile and brittle region can lead to the formation of vein type and altered rock type mineralization, e.g. Linglong, Denggezhuang and Jiaojia gold deposits. Both stages take place during the process of multi-stage emplacement and progressive deformation of ore-controlling shear zones. However, with the progressive deformation and uplift denudation of shear zones, the superposition of brittle deformation in the late stage may lead to the occurrence of multiple mineralization types in the same structural site, e.g. quartz vein type and altered rock type mineralization in Jiaojia gold deposit.

A Review on the Deposit Geology and Mineralization Mechanism of Tsumeb Polymetallic Deposit, Namibia

The Tsumeb polymetallic deposit of Otavi Mountain Land (OML), Namibia, is a prominent deposit of remarkable and complex mineral species with the accreditation of about 337 valid minerals. A total of 72 species of these minerals are of Tsumeb as the type of locality. The deposit was first prospected in 1893 by the South West Africa Company and it was mined from the year 1897 to 1996, yielding a total of about 30 Mt of ore with the grade of 10% Pb, 4.3% Cu, and 3.5% Zn along with ore minerals of As, Sb, Ag, Cd, and Au. The orebody also typifies the largest renowned single sulfidic accumulation of germanium (Ge). However, like many other deposits, the Tsumeb copper deposit has been exhausted. Hence, re-assessment of ore reserve and exploration is a crucial practice in the discovery of new mineral resources and occurrences. This practice requires extensive understanding of the geological characteristics and metallogenic mechanisms of the parent/exhausted ore deposit as a reference model. In this paper, we presented a summary description of the Tsumeb deposit (polymetallic Copper deposit) of the Otavi Mountain Land (OML), Namibia, with the main focus on the regional geological background, deposit geology and ore mineralization mechanism.

Super-enrichment mechanisms of precious metals by low-melting point copper-philic element (LMCE) melts

低熔点亲铜元素（LMCE）As、Sb、Bi、Hg、Pb、Se、Te、Tl、Sn等，均具有亲铜性、低熔点、半金属的特性，在成矿过程中可以形成LMCE熔体，并对Au、Ag、PGE等贵金属的高效富集沉淀起到一种重要的桥梁作用。作者对前人研究资料与LMCE热力学相图进行了分析，并结合浅成低温热液型、造山型、卡林-类卡林型、碱性-偏碱性侵入岩型金矿床的研究成果，探讨了LMCE熔体形成、类型及其对Au、Ag、PGE等贵金属富集成矿的机理，并提出了LMCE熔体参与成矿的矿物组合与结构特征标志。LMCE熔体可以在岩浆过程、（岩浆）热液过程及变质过程中形成，是贵金属矿床重要的成矿机制之一。LMCE熔体中存在大量原子团簇，团簇间的聚集生长会使熔体难以达到相平衡，形成许多非平衡矿物组合，如包含LMCE的自然元素、金属互化物及含LMCE的多相矿物。Au在LMCE熔体中也可以团簇存在，金团簇聚集形成球状或片状，并形成巨富的金矿体。LMCE熔体形成的矿物常以浑圆状、近浑圆状、不规则状的单个或群体组合的乳滴、珠滴、气泡的微粒包体产在硫化物、硒化物、碲化物、氧化物和硅酸盐矿物内或沿矿物裂隙线形排列，这些LMCE微粒包体是熔体扰动导致熔-熔或熔-液间发生乳化所致，流体沸腾是引起熔体扰动的主要机制。LMCE熔体不能快速淬火结晶，通常在低温下缓慢冷却达到相平衡，形成复杂的矿物组合，该特点即使在微米到纳米级的矿物微粒中也显著存在。熔体-流体包裹体是LMCE熔体参与成矿作用最为直接的证据。固溶体分解结构、熔体退火结构、矿物-熔体二面角结构、溶解-再沉淀结构等也是LMCE熔体参与成矿的标志性结构。;The low-melting point chalcophile elements (LMCE), including As, Sb, Bi, Hg, Pb, Se, Te, Tl, Sn and so on, have characteristics of chalcophile behavior, low melting point and semi-metallic properties, which can form LMCE melt during mineralization process and play an important role for the efficient enrichment and precipitation of Au, Ag, PGE and other precious metals. In this paper, the previous research data and the LMCE thermodynamic phase diagrams were analyzed. Combining research results of epithermal, orogenic, Carlin to Carlin-like and alkaline to meta-alkaline intrusion-related gold deposits, the authors discussed the formation and type of LMCE melts and their mechanisms for the enrichment of Au, Ag, PGE and other precious metals, and summarized mineral compositions and characteristic textures of mineralization that benefited by LMCE melts. The LMCE melts can be formed during magmatic, (magmatic-) hydrothermal and metamorphic processes, and belong to one of the important metallogenic mechanisms for precious metal deposits. There are many ion clusters in the LMCE melts, and aggregation between the clusters precludes the melt to reach phase equilibrium, which results in many non-equilibrium mineral combinations, including the coexistence of native LMCE, intermetallic compounds and multiphase minerals containing LMCE. Gold could also exist as ion clusters in the LMCE melt that gather to form spherical or flakes native gold, and form the super-rich ore bodies. The minerals formed by LMCE melt often exist as single or group combinations of emulsion droplets, beads, and bubbles in round, nearly round, and irregular particle inclusions in sulfides, selenides, tellurides, oxides and silicates, or distribute along fractures of minerals. These LMCE micro-inclusions are derived from melt disturbance that result in melt-melt or melt-liquid emulsification. Fluid boiling should be the main mechanism that causes the melt disturbance since the LMCE melt cannot be quenched and crystallized quickly at this process. It is usually cooled slowly at low temperature to achieve phase equilibrium and form complex mineral compositions. This feature is significant even in micro-to nano-scale mineral particles. Melt-fluid inclusions are the most direct evidence for the involvement of LMCE melts during mineralization. Solid solution decomposition texture, melt annealing texture, mineral-melt dihedral texture, dissolution-reprecipitation texture are also characteristic textures of LMCE melts involved in mineralization.

Sources of metallogenic materials and metallogenic mechanism of Tianbaoshan Pb-Zn deposit in Sichuan Province: Constraints from fluid inclusions and isotopic evidences

天宝山铅锌矿床位于扬子地台西缘，为川滇黔铅锌矿集区具有代表性大型铅锌矿床，其金属储量(Pb+Zn)可达2.6Mt，铅锌品位10%~15%。本文在系统的分析流体包裹体和C、H、O、S、Pb、Sr同位素研究的基础上，确定其成矿物质来源、成矿流体性质及来源，并探讨其成矿机制。H-O同位素及流体包裹体研究表明，成矿流体具有中低温(均一温度峰值为140~200℃)及中低盐度(盐度峰值为6%~12% NaCleqv)的特征。灯影组白云岩与海相沉积碳酸盐岩的C、O同位素组成较为相似，热液方解石与含矿白云岩O同位素组成均稍低于灯影组白云岩，表明成矿流体中的CO₂可能来源于海相碳酸盐岩的溶解。矿区硫化物<i>δ</i>³⁴S值介于1.1‰~7.5‰之间，表明S主要来源于灯影组中硫酸盐热化学还原作用和岩浆硫的混合。矿石硫化物的Pb同位素比值在Pb演化图解上主要落入上地壳与造山带之间，表明Pb具有壳源特征，成矿物质来源主要来自于盖层沉积岩和基底地层。闪锌矿的⁸⁷Sr/⁸⁶Sr值(0.71099~0.71856)及热液方解石⁸⁷Sr/⁸⁶Sr值(0.71014~0.71169)均高于灯影组白云岩⁸⁷Sr/⁸⁶Sr值(0.70773~0.71026)，表明成矿流体流经了具有高⁸⁷Sr/⁸⁶Sr值的基底地层，并与其发生水岩反应及同位素交换。

Mineralogy of Nickel and Cobalt Minerals in Xiarihamu Nickel–Cobalt Deposit, East Kunlun Orogen, China

Located in the East Kunlun Orogen, China, the Xiarihamu magmatic nickel–cobalt sulfide deposit is the country’s second largest deposit of this type. It was formed in special early Paleozoic with low copper grade (0.14 wt%) compared with other deposits of the same type. The mineralogy of nickel and cobalt minerals, which are direct carriers of these elements, can clearly reflect their behavior in the process of mineralization; however, such information for this deposit remains unreported. In the present study, we use an electron microscope and electron probe microanalyzer to delineate and analyze many nickel and cobalt minerals such as maucherite, nickeline, cobaltite, violarite, gersdorffite, parkerite, and arsenohauchecornite in various rocks and ores. With the increase in crustal material contamination, it can reach arsenide saturation locally in sulfide melt, then a separate Ni-rich arsenide (bismuth) melt exsolves somewhere. This melt will crystallize into nickeline, parkerite, arsenohauchecornite, and maucherite first. Second, most of nickel and cobalt tend to enter cobaltite and pentlandite phases, rather than existing in chalcopyrite and pyrrhotite phases as isomorphism during sufficient fractional crystallization of sulfide melt, which gathered nickel and cobalt elements widely. Also, more than one magma might result in the superposition of ore-forming elements. Later, the ore-forming elements redistribute limitedly through a hydrothermal process. The metallogenic mechanism model of nickel and cobalt established in the present study not only explains the process of nickel–cobalt mineralization in Xiarihamu but also can be applied to similar deposits and has a wide universal replicability.

Ore‐forming Fluid and Metallogenic Mechanism of Wolframite–Quartz Vein‐type Tungsten Deposits in South China

AbstractSouth China is endowed with copious wolframite–quartz vein‐type W deposits that provide a significant contribution to the world's tungsten production. Mineralization is spatially associated with highly evolved granites, which have been interpreted as products of ancient crustal anatexis. Ore veins are mainly hosted in low‐grade metamorphosed quartz sandstone, slate and granitic rocks. The ore minerals mainly comprise wolframite, cassiterite, scheelite and pyrite, with minor molybdenite, arsenopyrite and chalcopyrite. Typical steeply dipping veins can be divided into five zones from top to the bottom, namely: (I) thread, (II) veinlet, (III) moderate vein, (IV) thick vein, and (V) thin out zones. In general, three types of fluid inclusions at room temperature are commonly recognized in wolframite and/or quartz from these veins: two‐phase liquid‐rich (type L), two‐phase CO2‐bearing (type CB), and CO2‐rich (type C). Comparative microthermometry performed on fluid inclusions hosted in wolframite and associated quartz indicates that most wolframite was not co‐precipitated with the coexisting quartz. Detailed petrographic observation and cathodoluminescence (CL) imaging on coexisting wolframite and quartz of the Yaogangxian deposit, show repeated precipitation of quartz, wolframite, and muscovite, suggesting a more complex fluid process forming these veins. Previous studies of H‐O isotopes and fluid inclusions suggested that the main ore‐forming fluids forming the wolframite–quartz vein‐type deposits had a magmatic source, whereas an unresolved debate is centered on whether mantle material supplemented the ore‐forming fluids. The variable CO2 contents in the ore‐forming fluids also implies that CO2 might have had a positive effect on ore formation. Fluid inclusion studies indicate that wolframite was most likely deposited during cooling from an initial H2O + NaCl ± CO2 magmatic fluid. In addition, fluid‐phase separation and/or mixing with sedimentary fluid might also have played an important role in promoting wolframite deposition. We speculate that these processes determine the precipitation of W to varying degrees whereas the leading mechanistic cause remains an open question. Comprehensive studies on spatial variation of fluid inclusions show that both the steeply and gently dipping veins are consistent with the “five floors” model that may have broader applications to exploration of wolframite–quartz vein‐type deposits. Recent quantitative analysis of wolframite‐ and quartz‐hosted fluid inclusions by laser ablation inductively‐coupled plasma mass spectrometry shows enhanced advantages in revealing fluid evolution, tracing the fluid source and dissecting the ore precipitation process. Further studies on wolframite–quartz vein‐type W deposits to bring a deeper understanding on ore‐forming fluids and the metallogenic mechanism involved.